Such flow heaters are used to heat fluids (i.e., especially liquids and/or gases) and are used, for example, in dishwashers, steam cookers or washing machines and are known, for example, from DE 42 26 325 C1.
Prior-art flow heaters usually have a metal section, in which a tube for passing through a fluid to be heated is mounted. One or more adjacent tubular heating bodies, which are likewise mounted in the metal section, are arranged around the tube outside the tube interior space thereof. To guarantee a direct and close contact between the metal section and tubular heating body, on the one hand, and the metal section and tube for passing through a fluid to be heated, on the other hand, the arrangement is mostly fully or partly compressed.
The requirement on the performance of such flow heaters has noticeably increased over the last few years. It was found that the flow heaters of conventional design, as they are known from the state of the art, reach their limits with the use of tubular heating bodies of ever-increasing performance, because sufficient heat transfer into the fluid is no longer guaranteed. This leads to an unacceptably high temperature on the outside of the flow heater and in the extreme case to melting of the metal section.
In a second class of flow heaters, which are known, e.g., from DE 1 036 816 A1, a tubular heating body is arranged in the interior of a tube for passing through a fluid to be heated. Thus, it is in direct contact with the fluid, which significantly increases the risk of failure of the tubular heating body as a consequence of the interaction thereof with the fluid, because local deposits, for example, calcifications, which hinder the dissipation of heat and lead to destruction of the tubular heating body, occur in the systems used in practice in a number of applications. If corrosive media are heated, the direct contact with the fluid may likewise damage the tubular heating body. In addition, especially if they are used with high surface loads and low flow velocities, such flow heaters may cause bubbling in liquids to be heated, which will likewise lead to a local hindrance of the dissipation of heat and entails the risk of destruction.